Solar or wind energy-based systems as well as flow batteries provide solutions to the ever increasing need for the low cost generation and storage of electricity. A flow battery that uses hydrogen and a halogen ion, such as for example bromine, as active materials was invented in 1961 by the National Aeronautics and Space Administration. This type of flow battery demonstrates a high power density, i.e. it can store or release a high power per unit of membrane area. A flow battery relying on hydrogen and a halogen ion can indeed reach a power density of 10 kW·m−2, which is 20 times higher than the power density of typical vanadium redox flow batteries. Since 1961, several research groups and companies have investigated cells in which the hydrogen reactant gas is kept at a constant and nearly atmospheric pressure. The hydrogen gas released during charging of the flow battery assembly is either compressed outside the electrochemical flow battery assembly by an external compressor or it is stored at low pressure in a large storage tank. A hydrogen compressor is typically a technically challenging and energy inefficient device, which requires high purchase and maintenance costs. This use of an external mechanical compressor therefore increases the costs associated with the system, reduces its long-term reliability and reduces its efficiency.
WO2011089518 is a patent application from by Ramot at Tel-Aviv University Ltd., filed on Jan. 24, 2011, which describes a system capable of conducting both hydrogen evolution reactions and hydrogen oxidation reactions in the same flow battery assembly. The patent application WO2011089518 describes a system in which the pressure in the hydrogen chamber is maintained at a higher value than in the electrolyte chamber, as well as the method implemented to maintain this pressure difference between the hydrogen chamber and the halogen chamber within a stack of battery cells. The method described in WO2011089518 comprises sensing the pressures in the hydrogen chamber and the electrolyte chamber within a stack of battery cells and adapting the pressure of the electrolyte entering the stack of battery cells in order to maintain the desired pressure difference between the hydrogen chamber and the electrolyte chamber within the stack of battery cells. The pressure in the electrolyte chamber is therefore continuously controlled in function of the pressure in the hydrogen chamber, which makes the use of the flow battery assembly complicated and requires the implementation of extra components such as pumps and sensors which increases the cost associated with such an assembly and reduces its robustness because of an increased risk of component failure. Moreover, even though the patent application WO2011089518 lists advantages associated with maintaining a pressure difference between the hydrogen chamber and the electrolyte chamber, such a control method implementing a tight control of this pressure difference within acceptable limits is deemed necessary in order to avoid damage to the membrane.
WO2013086100 is a patent application from by Sun Catalytix Corp., filed on Dec. 6, 2012 and published on Jun. 13, 2013, which describes a method comprising passing a current through a battery cell in order to produce a partial pressure of the hydrogen in the hydrogen chamber of 200-250 pound-force per square inch gauge, i.e. a maximum pressure 18.25 bar relative to ambient. The method further comprises controlling the pressure in the electrolyte chamber to make it substantially similar or at a predetermined small pressure differential relative to the pressure in the hydrogen chamber. The hydrogen chamber of each battery cell comprises a hydrogen electrode connected to a controllable outlet that is coupled to a control device which is capable of maintaining a predetermined pressure within the hydrogen chamber by suitably controlling this outlet. This requires a manual intervention in order to pre-select the value of the pressure in the hydrogen chamber, which makes the use of the flow battery assembly less reliable. The control of the pressure in the hydrogen chamber further requires the implementation of components such as pumps and sensors, which increases the costs associated with such a flow battery assembly. Although no external hydrogen compressor is required in the hydrogen circuit, similar elements are now required in the electrolyte circuit in order to maintain the pressure difference within acceptable limits in order to avoid damage to the membrane of the battery cell.
WO2007/072096 is a patent application from by H-Cella Inc., filed on Dec. 22, 2006 and published on Jun. 28, 2007, which describes a porous electrode used in an electrochemical cell operating with high differential pressure difference. In the context of the system described in WO2007/072096 a fuel cell is understood as a device or equipment which comprises two electrodes such that, during operation of the fuel cell, hydrogen reacts on the anode and oxygen reacts on the cathode. With the help of a catalytic agent, the hydrogen molecules break up into protons and electrons, and the electrons arriving at the cathode combine with the protons and with the oxygen molecules creating water as a final product. It is clearly stated in WO2007/072096 that if a reversed process to electrolysis takes place, that is if hydrogen gas and oxygen gas react to each other on the electrodes and in the course of this electric current is produced, then the system is called a fuel cell. The fuel cell described in WO2007/072096 therefore relies on the consumption of two gases, hydrogen and oxygen, and the reaction between the two gases results in the production of water. The difference occurring between the amounts of gases generated in the course of electrolysis results in significant pressure difference on the two sides of the membrane of the fuel cell. Indeed, as the amount of gas H2 generated on the cathode is twice as much as the amount of O2 generated on the anode, the gas pressure on the cathode side presses the membrane against the anode. The fuel cell described in WO2007/072096 therefore undergoes a high gas pressure and a high gas pressure difference, where the differential pressure difference relates to the pressure difference occurring in respect of the gases generated in the space of the two electrodes on the one part, and the high pressure difference occurring between the internal space of the fuel cell and the external space. WO2007/072096 does not describe a system in which a cell withstands a pressure difference between a gas and a liquid electrolyte without O2 gas, where an electrolyte is a substance that ionizes when dissolved in suitable ionizing solvents, and which can transmit electric current through positively and negatively charged ions. The fuel cell described in WO2007/072096 is therefore not compatible with a flow battery assembly relying on the consumption of a gas and a liquid electrolyte which does not comprise O2 gas.
The fuel cell described in WO2007/072096 operates with two gases, hydrogen and oxygen, and the reaction between the two gases produces water. The fuel cell described in WO2007/072096 therefore undergoes a high gas pressure and a high gas pressure difference, where the differential pressure difference relates to the pressure difference occurring in respect of the gases generated in the space of the two electrodes on the one part, and the high pressure difference occurring between the internal space of the fuel cell and the external space. It is clear that a hydrogen-redox flow battery assembly cannot be considered as a fuel cell of the type described in WO2007/072096, as a hydrogen-redox flow battery assembly operates with hydrogen and a liquid electrolyte, where the liquid electrolyte is a substance that ionizes when dissolved in suitable ionizing solvents, and which can transmit electric current through positively and negatively charged ions, and where the reaction between the liquid electrolyte and hydrogen produces an electrolyte, but not water or oxygen gas.
It is an objective of the present invention to disclose a flow battery assembly that overcomes the above identified shortcomings of existing tools. More particularly, it is an objective to disclose such flow battery assembly for generating and storing electric power in a simpler, more robust, faster, more efficient, safer, more reliable and more economical manner.